Oil Pollution is Making Gulf Dolphins Sick

For eighty-seven days in 2010, 210 million gallons of oil from wells below the Deepwater Horizon poured into the Gulf of Mexico. Researchers announced recently that as a result, Bottlenose dolphins in Louisiana’s Barataria Bay are suffering from a host of maladies, including lung disease and adrenal problems.

For eighty-seven days in 2010, 210 million gallons of oil from wells below the Deepwater Horizon poured into the Gulf of Mexico. Researchers announced recently that as a result, Bottlenose dolphins in Louisiana's Barataria Bay are suffering from a host of maladies, including lung disease and adrenal problems. They're also losing their teeth. The research was conducted in August 2011, by a team of governmental, academic, and non-governmental scientists as part of the post-spill Natural Resource Damage Assessment.

To understand what the effects of oil contamination were on marine mammals like dolphins and whales, the team conducted health assessments on thirty-two Barataria Bay dolphins in 2011, a site chosen because that area was heavily oiled during and after the spill. The team compared those dolphins to twenty-seven from Sarasota Bay, Florida, where researchers were already conducting a decades-long study of dolphin health, and which was lucky enough to remain oil-free following the blowout.

The team sampled each dolphin's blubber, collected blood and urine samples, conducted ultrasounds, took body-size measurements, and more. The results were published in December in the journal Environmental Science and Technology.

“There’s disease in any wild population,” said lead researcher Lori H. Schwacke, branch chief of the National Oceanic and Atmospheric Administration’s Centers for Coastal Ocean Science. “But we just haven’t seen animals that were in such bad shape as what we saw in Barataria Bay.”

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The researchers were particularly surprised to find that the Barataria Bay dolphins had unusually low levels of the adrenal hormones cortisol and aldosterone, compared with the Sarasota dolphins. When faced with a stressful situation, the adrenal glands typically pump out hormones, which in turn increase heart rate and blood sugar, preparing the animal for a fight-or-flight response. That response allows the dolphins to respond appropriately to stressful or threatening situations, such as being attacked by a predator.

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About 25 percent of the Barataria Bay dolphins were also found to be significantly underweight in comparison with just one of the Sarasota Bay dolphins. Many had low blood sugar, and several had low red blood cell counts. For six of the Barataria Bay dolphins — but none of those from Sarasota Bay — blood tests revealed liver abnormalities.

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“Some of the animals’ lung disease [was] so severe that we did consider those conditions life-threatening,” said researcher Cynthia R. Smith, executive director and director of medicine for the National Marine Mammal Foundation. At least one of the dolphins that the team examined died about five months later; a necropsy resulted in the relatively rare diagnosis of bacterial pneumonia.

It's worth pointing out that the cetacean populations in the northern Gulf of Mexico are stranding in record numbers, something that NOAA refers to as an "unusual mortality event," or UME. What's interesting is that the UME began several months before the Deepwater Horizon blowout.

What the research makes clear, especially by comparing the Barataria Bay dolphins to those from Sarasota, is that the oil contamination is seriously affecting the health of marine mammals (and other marine life as well). But some parts of the Gulf, including Louisiana's Barataria Bay, were already bad news for dolphins and other animals. The oil is but one from an array of environmental stressors and pollutants, which also includes shipping noises, toxic algal blooms, other types of industrial runoff, and more.

The views expressed are those of the author(s) and are not necessarily those of Scientific American.

ABOUT THE AUTHOR(S)

Jason G. Goldman

Jason G. Goldman is a science journalist based in Los Angeles. He has written about animal behavior, wildlife biology, conservation, and ecology for Scientific American, Los Angeles magazine, The Washington Post, The Guardian, the BBC, Conservation magazine, and elsewhere. He contributes to Scientific American's "60-Second Science" podcast, and is co-editor of Science Blogging: The Essential Guide (Yale University Press). He enjoys sharing his wildlife knowledge on television and on the radio, and often speaks to the public about wildlife and science communication.

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